/*
 * Lazy Load - jQuery plugin for lazy loading images
 *
 * Copyright (c) 2007-2012 Mika Tuupola
 *
 * Licensed under the MIT license:
 *   http://www.opensource.org/licenses/mit-license.php
 *
 * Project home:
 *   http://www.appelsiini.net/projects/lazyload
 *
 * Version:  1.8.0
 *
 */
(function ($, window) {
    var $window = $(window);

    $.fn.lazyload = function (options) {
        var elements = this;
        var $container;
        var settings = {
            threshold     :0,
            failure_limit :0,
            event         :"scroll",
            effect        :"show", // 显示效果
            container     :window,
            data_attribute:"original",
            skip_invisible:true,
            appear        :null,
            load          :null
        };

        function update() {
            var counter = 0;

            elements.each(function () {
                var $this = $(this);
                if (settings.skip_invisible && !$this.is(":visible")) {
                    return;
                }
                if ($.abovethetop(this, settings) || $.leftofbegin(this, settings)) {
                    /* Nothing. */
                } else if (!$.belowthefold(this, settings) &&
                    !$.rightoffold(this, settings)) {
                    $this.trigger("appear");
                } else {
                    if (++counter > settings.failure_limit) {
                        return false;
                    }
                }
            });

        }

        if (options) {
            /* Maintain BC for a couple of versions. */
            if (undefined !== options.failurelimit) {
                options.failure_limit = options.failurelimit;
                delete options.failurelimit;
            }
            if (undefined !== options.effectspeed) {
                options.effect_speed = options.effectspeed;
                delete options.effectspeed;
            }

            $.extend(settings, options);
        }

        /* Cache container as jQuery as object. */
        $container = (settings.container === undefined || settings.container === window) ? $window : $(settings.container);

        /* Fire one scroll event per scroll. Not one scroll event per image. */
        if (0 === settings.event.indexOf("scroll")) {
            $container.bind(settings.event, function (event) {
                return update();
            });
        }

        this.each(function () {
            var self = this;
            var $self = $(self);

            self.loaded = false;

            /* When appear is triggered load original image. */
            $self.one("appear", function () {
                if (!this.loaded) {
                    if (settings.appear) {
                        var elements_left = elements.length;
                        settings.appear.call(self, elements_left, settings);
                    }
                    $("<img />").bind("load", function () {
                        $self.hide().attr("src", $self.data(settings.data_attribute))[settings.effect](settings.effect_speed);
                        self.loaded = true;

                        /* Remove image from array so it is not looped next time. */
                        var temp = $.grep(elements, function (element) {
                            return !element.loaded;
                        });
                        elements = $(temp);

                        if (settings.load) {
                            var elements_left = elements.length;
                            settings.load.call(self, elements_left, settings);
                        }
                    }).attr("src", $self.data(settings.data_attribute));
//                    console.log($self.data(settings.data_attribute));
                }
            });

            /* When wanted event is triggered load original image */
            /* by triggering appear.                              */
            if (0 !== settings.event.indexOf("scroll")) {
                $self.bind(settings.event, function (event) {
                    if (!self.loaded) {
                        $self.trigger("appear");
                    }
                });
            }
        });

        /* Check if something appears when window is resized. */
        $window.bind("resize", function (event) {
            update();
        });

        /* Force initial check if images should appear. */
        update();

        return this;
    };

    /* Convenience methods in jQuery namespace.           */
    /* Use as  $.belowthefold(element, {threshold : 100, container : window}) */

    $.belowthefold = function (element, settings) {
        var fold;

        if (settings.container === undefined || settings.container === window) {
            fold = $window.height() + $window.scrollTop();
        } else {
            fold = $(settings.container).offset().top + $(settings.container).height();
        }

        return fold <= $(element).offset().top - settings.threshold;
    };

    $.rightoffold = function (element, settings) {
        var fold;

        if (settings.container === undefined || settings.container === window) {
            fold = $window.width() + $window.scrollLeft();
        } else {
            fold = $(settings.container).offset().left + $(settings.container).width();
        }

        return fold <= $(element).offset().left - settings.threshold;
    };

    $.abovethetop = function (element, settings) {
        var fold;

        if (settings.container === undefined || settings.container === window) {
            fold = $window.scrollTop();
        } else {
            fold = $(settings.container).offset().top;
        }

        return fold >= $(element).offset().top + settings.threshold + $(element).height();
    };

    $.leftofbegin = function (element, settings) {
        var fold;

        if (settings.container === undefined || settings.container === window) {
            fold = $window.scrollLeft();
        } else {
            fold = $(settings.container).offset().left;
        }

        return fold >= $(element).offset().left + settings.threshold + $(element).width();
    };

    $.inviewport = function (element, settings) {
        return !$.rightofscreen(element, settings) && !$.leftofscreen(element, settings) &&
            !$.belowthefold(element, settings) && !$.abovethetop(element, settings);
    };

    /* Custom selectors for your convenience.   */
    /* Use as $("img:below-the-fold").something() */

    $.extend($.expr[':'], {
        "below-the-fold" :function (a) {
            return $.belowthefold(a, {threshold:0});
        },
        "above-the-top"  :function (a) {
            return !$.belowthefold(a, {threshold:0});
        },
        "right-of-screen":function (a) {
            return $.rightoffold(a, {threshold:0});
        },
        "left-of-screen" :function (a) {
            return !$.rightoffold(a, {threshold:0});
        },
        "in-viewport"    :function (a) {
            return !$.inviewport(a, {threshold:0});
        },
        /* Maintain BC for couple of versions. */
        "above-the-fold" :function (a) {
            return !$.belowthefold(a, {threshold:0});
        },
        "right-of-fold"  :function (a) {
            return $.rightoffold(a, {threshold:0});
        },
        "left-of-fold"   :function (a) {
            return !$.rightoffold(a, {threshold:0});
        }
    });

})(jQuery, window);